Various powders exemplified by white and colored pigments such as titanium oxide, zinc oxide, red iron oxide, and the like and extender pigments such as mica, sericite, and the like are widely used in the fields of basic cosmetic compositions and other various cosmetic compositions such as sunscreens, nail colors, nail coats, foundations, mascaras, eye liners, and the like. However, untreated powder is prone to agglomerate due to the electric charge and polarity, trace amount of impurities, and the like on the powder surface. Therefore, powders that have been subject to various surface treatments are widely used for the purpose of enhancing dispersibility and stability of a powder in a cosmetic composition and also improving the tactile sensation, moisture resistance, sebum resistance, and the like of a cosmetic composition comprising a powder.
Known examples of such surface treatments include lipophilization treatments using an oil agent, a metal soap, or the like; hydrophilization treatments using a surfactant, water-soluble polymer, or the like; hydrophobization treatments using silicone compounds; silica treatments; alumina treatments; and the like. Particularly, in recent years, there have been many cases where a surface treatment using a silicone compound having a reactive moiety in the molecule has been performed. The reactive site forms a chemical bond with the powder surface and, as a result, surface treatment using the silicone compound is effective from the perspective of simultaneously modifying the surface of the powder and blocking the surface activity of the powder without substantially changing the characteristics of the powder itself. In addition, because surface treatment can be performed reliably, the treatment agent will not separate from the powder surface, even when compounded in a cosmetic composition comprising a solvent. An example of such a surface treatment is a method in which a powder is surface treated using a methylhydrogenpolysiloxane (Patent Document 1). However, in this method, unreacted Si—H groups still remain even after the surface treating of the powder and, therefore, there is a problem when this powder is compounded in a cosmetic composition because hydrogen gas may be produced depending on the components and the like in the cosmetic composition.
On the other hand, methods for manufacturing a powder dispersion using a hydrophilic modified organopolysiloxane that has good compatibility with the powder surface have been proposed. Examples thereof include a method for forming a polyether-modified organopolysiloxane into a powder dispersing aid (Patent Document 2) and a method for forming an organopolysiloxane modified by polyglycerine or a similar polyhydric alcohol into a powder dispersing aid (Patent Document 3). However, there are problems in that the powder dispersion effectiveness is still insufficient, viscosity of a power dispersion obtained by dispersing a powder in silicone oil or a similar oil agent increases gradually over time, fluidity is lost, and the like.
As a method to resolve the problems described above, the present applicant has proposed methods using a co-modified organopolysiloxane copolymer having a group that has a carbosiloxy dendron structure and a glycerin derivative, polyhydric alcohol, or similar hydrophilic group in the molecule (Patent Documents 4, 5 and 6). Such co-modified organopolysiloxanes are safe and do not produce hydrogen, and can be advantageously used in the surface treating of a powder. Moreover, affinity with other raw materials of cosmetic compositions is superior, and the dispersibility and stability of the powder in a cosmetic composition comprising a powder can be enhanced.
In general, in formulations primarily containing a silicone as an oil agent, the feel is sometimes too light due to the characteristics of the silicone. However, in order to meet the wide-ranging needs of consumers, it is necessary to prepare cosmetic compositions having a variety of feels, and formulations having a heavy feel are also sometimes preferable in order to give an impression of elegance, in particular. In the preparation of such agents, formulations based on various hydrocarbon solvents such as oil agents other than silicone including isododecane, for example, are also being actively developed. However, the co-modified organopolysiloxane described above has a molecular design primarily suited to a silicone-based formulations, so there is a problem in that the co-modified organopolysiloxane does not demonstrate the desired dispersibility in hydrocarbon solvents. Accordingly, the development of silicone-based active agents and dispersants compatible with hydrocarbon solvents has become extremely important.
In order to solve the problems described above, there are alkyl-modified silicone polyethers, which are also advantageous from the perspective of cost (Patent Document 7). The co-modified organopolysiloxane copolymers described above are not only used as emulsifiers, but are also used as dispersants and are applied to various powder cosmetic compositions. However, all of these copolymers have a relatively high molecular weight and a large number of hydrophilic groups, so there are problems in that the dispersibility with respect to fine particle powders is low, and the copolymers tend to become sticky when included in formulations.